1. Field of the Invention
The invention generally relates to inline capacitors. More particularly, the invention relates to a compact coaxial in-line capacitor assembly.
2. Description of Related Art
Electrical cables, for example the coaxial transmission lines interconnecting transceiver equipment with antenna towers, are equipped with surge suppression equipment to provide an electrical path to ground for diversion of electrical current surges resulting from, for example, static discharge and or lightning strikes.
In-line surge suppression assemblies typically incorporate a frequency selective shorting element such as an inductive coil or stub between the inner and outer conductors of a coaxial cable. To prevent lower frequency and or direct current from being passed to down line equipment a physical break is inserted in the form of an in-line capacitor. The high frequency capacitive coupling across the capacitor is configured to pass only the desired operating frequencies of the system.
Prior in-line capacitor assemblies have utilized conventional electronic component packages such as ceramic disc or SMD ceramic chips that are mounted by soldering or adhesive mounting within a cavity of a shielding enclosure. The resulting assemblies have limited power ratings, are fragile, expensive to manufacture and introduce a significant impedance discontinuity to the associated coaxial line. In particular, the adhesives SMD capacitors rely on to maintain their position on the center conductor can soften and shift due to high operating temperatures generated by the RF power passing through the device. Any shift in position can permanently adversely affect the designed capacitance.
Another prior inline capacitor solution is to form a capacitor of the desired value in-line by inserting a dielectric spacer between two mating planar or cylindrical pin into socket mating ends of the inner conductor. The capacitance resulting from these solutions is determined by the dielectric value of the spacer material, the gap distance and surface area of the mating surfaces. The resulting modules make tradeoffs between power handling capability, impedance discontinuity and size. Further, these solutions require significant supporting structure to maintain the alignment of the inner conductor mating surfaces.
Increases in the number of different simultaneous frequency bands carried by a single coaxial cable, for example for cellular voice and data communications applications, has created demand for compact, inexpensive high power capacity in-line capacitors as primary elements of coaxial surge protection and or dc-bias assemblies.
Competition within the electrical cable, connector and associated accessory industries has focused attention on performance improvements and cost reductions resulting from new materials and manufacturing efficiencies, reduced installation requirements and simplification/overall number of discrete parts reduction.
Therefore, it is an object of the invention to provide an apparatus that overcomes deficiencies in the prior art.